Jurgen Melzer handed Roger Federer only his fifth loss of the season as the Austrian came through in a virtual sandstorm with a 6-4, 6-4 quarterfinal victory on Friday at the Monte Carlo Masters.
Federer, a three-time finalist in 2006-2008 against Rafael Nadal, was well off his best form after two superlative previous matches this week in the principality as he began his season on clay.
The Swiss was quick to admit he was outplayed on the day as he missed on too many chances.
"I don't think I played terrible, it's still the first week of clay, so I don't expect myself to play my very best.
"He played well when he had to and I missed too many chances, Every time I had this slight opening, things didn't go my way. Either he shanks them and they stay in play, he hits the line.
"I try to do something, I miss by a little bit. All those things accumulate to something quite frustrating. That's what made it hard. But he did well, played aggressive and played the right way he was supposed to."
Melzer added the final major scalp to his record and was pleased with the result, especially after being forced to leave the court after just one game for physio treatment of a neck problem.
"I felt it when I played a backhand, it kind of blocked my spine," said Melzer of his early incident. "But the physio did a great job unblocking it.
"I was a little worried. But then the pain like go away quickly, it didn't bother me at all."
The Austrian also said he was pleased to have finally defeated Federer. "I beat Rafa last year (Shanghai). I have beaten Nole (Djokovic, French Open quarter-finals). So this was the one missing. I'm very happy I actually did it today."
"It was a tough match for me, he beat me three times last year and I didn't even win a set. But many things went well for me, my shots worked well. When he had break points I was calm and served well.
"I did well on the big points and played my game."
Spain's fourth seed David Ferrer will face Melzer in the semis after defeating Serb Viktor Troicki 6-3, 6-3.
Federer stands 24-5 this season with his losses coming three times to Novak Djokovic and once to Rafael Nadal before Melzer. Melzer was playing his first Monte Carlo quarter-final.
Federer was plagued by 24 unforced errors while Melzer notched 26. The Swiss was unsuccessful on all seven of his break points in the challenging conditions.